A dynamic photoelastic study of stress waves generated by multiple dilatational sources in a half plane is described. The model material is CR-39 and lead azide charges are used to produce the dilatational waves. Fringe patterns are recorded by a multiple spark gap camera. Interactions between the waves before and after reflection from the free surface are studied. The effect of varying the distance between sources and their depth below the free surface is investigated in some detail. (Author).

This Bureau of Mines publication reviews the research conducted under a 3-year, $6.6 million program in rock mechanics and rapid excavation. The program was sponsored by the Defense Department's Advanced Research Projects Agency and was managed by the Bureau. In addition to the rock mechanics investigations, projects were funded in the following general areas of rapid excavation: System analysis, geologic prediction, rock disintegration, ground support, and materials handling. This report briefly summarizes the significant technical accomplishments of the individual research projects and references the contract reports and other publicatons where more detailed descriptions of the research can be obtained.